Various kinds of treatment apparatuses are known that comprise a treatment unit to be supplied with a fluid. The known treatment apparatuses include, for example, blood treatment apparatuses. During the blood treatment, the patient's blood flows in an extracorporeal blood circuit through the blood treatment unit. In the case of apparatuses for haemodialysis, haemofiltration and haemodiafiltration, the blood treatment unit is a dialyser or filter, which is divided by a semi-permeable membrane into a blood chamber and a dialysing fluid chamber. During the dialysis treatment, the blood flows in an extracorporeal blood circuit through the blood chamber, whilst the dialysing fluid flows in a dialysing fluid circuit through the dialysing fluid chamber of the dialyser.
Considering the large exchange quantities, there is a need with the known methods and apparatuses for blood treatment for exact balancing of the fluid removed from the patient and the fluid fed to the patient during the overall treatment time. Gravimetric and volumetric balancing devices are known.
In order to be able to ensure a continuous flow of dialysing fluid through the dialysing fluid chamber of the dialyser, two balancing chambers are in practice connected in parallel, which supply the dialyser alternately with fresh dialysing fluid. A balancing unit with two balancing chambers is described in for example DE 28 38 414.
Because of the large fluid requirement in dialysis, the preparation of the dialysate from concentrates and pure water (RO water) in the machine has evolved, in order to avoid the storage of fairly large quantities of solutions. The RO water is made available centrally in the clinic and distributed via lines to the dialysis machines in the dialysis stations. In the treatment of an acute renal insufficiency, such as can occur for example after accidents, which calls for intensive-care support for the patient, an RO water connection is generally not present. The dialysing fluid is then made available to the machine by means of containers, for example canisters or bags.
Apparatuses for extracorporeal blood treatment are known, wherein the balancing unit for balancing fresh dialysing fluid against used dialysing fluid is a component part of an article (disposable) intended for one-off use, which is inserted into a suitable receiving unit of the blood treatment apparatus. Balancing units constituted as a disposable are described in for example DE 198 30 928 C1 and DE 195 46 028 C2. In order to balance fresh dialysing fluid against used dialysing fluid, the known disposables comprise chambers which are filled with fresh used dialysing fluid.
For the control of the extracorporeal blood treatment apparatus, it is necessary to measure the pressure at various points of the fluid system. The pressure measurement should take place with a non-invasive procedure, in order to reduce the risk of contamination of the fluid system.
Devices for measuring the pressure in fluid systems are known in extracorporeal blood treatment apparatuses. Pressure measuring devices are known that comprise a pressure sensor which is disposed not in, but rather outside the fluid system. The pressure sensor of the known pressure measuring devices is disposed in a pressure measuring line leading away from the fluid system, behind a hydrophobic sterile filter located in the line that is permeable to air, but impermeable to liquid. The pressure sensor consequently measures the pressure in the air column behind the sterile filter.
Especially in the case of balancing devices constituted as a disposable, a pressure measurement taken with additional elements that are disposed outside the disposable proves to be disadvantageous. The drawbacks result not only from the additional components, but also from additional connections that have to be created when the disposable is connected to the blood treatment apparatus. The creation of these connections not only requires additional labor expenditure, but also increases the risk of malfunctions occurring during the blood treatment.
In order to ameliorate these disadvantages relating to pressure measurements the invention described herein simplifies the pressure measurement in the fluid system of a device for conveying a fluid to a filter unit of a medical treatment apparatus, in particular for conveying a fluid to a blood treatment unit of an extracorporeal blood treatment apparatus.